1. Field of the Invention
The present invention relates to the field of vehicle positioning systems that can be used to ascertain whether a vehicle is positioned within a lane on a roadway. More specifically, the present invention is directed to a vehicle positioning system that integrates global positioning system (GPS) data with other navigational data to determine in a real-time, robust and precise manner a lane position of the vehicle on a mapped roadway for lane departure detection.
2. Description of the Related Art
Many different on-road vehicle systems exist or are being developed to address individual applications such as lane-keeping, lateral collision avoidance, intersection collisions, route planning, traffic management, collision notification, automated control, etc. Each of these systems varies in performance and implementation challenges. Both commercial and government activities continue to address the problem of combining systems designed for specific applications to provide low cost, integrated vehicle systems which can significantly increase driver and vehicle safety. GPS has significant potential for enabling a variety of transportation user services.
Prior art systems have used a variety of methods to determine and maintain the position of a vehicle with precision. One type, through the use of optical systems, uses cameras and visualization techniques to follow lane boundaries. The benefits of such optical systems are that they have a relatively low cost, are based on existing technology and use existing lane markers. Optical systems have problems related to reliability due to paint differences, weather, exit lanes, etc. Other methods to determine and maintain the position of a vehicle with precision are magnetic sensor systems. In such a system, the vehicle follows magnets or magnetic pavement marking tape along lane boundaries. Such systems have a relatively low cost since they use low cost magnetic sensors and electronics and are largely not adversely impacted by weather. However, such systems require a great deal of infrastructure and upkeep, have reliability issues due to missing sensors and are impacted by the presence of large metallic objects in the area, as well as by trucks and buildings.
Other prior art systems used to determine and maintain the position of a vehicle with precision utilize driver based sensors. Such systems detect drowsiness from driver characteristics such as eye movement and/or wheel motion. Such systems have the benefit in that they can often identify the state of the driver prior to lane departure but are hampered by reliability problems due to operator differences and false alarms and do not benefit from an actual road position. RF systems are also used to detect lane position through the input of RF signals along lane/road boundaries. The RF systems are useful in all weather environments but require a great amount of infrastructure and upkeep required for the RF emitters along the road.
GPS and Differential GPS (DGPS) have also been used in prior art systems to determine and maintain the position of a vehicle with precision. In such prior art systems, the actual vehicle position is compared to surveyed lane boundaries through the use of GPS data. Such systems have the benefits of being useful in all weather, use existing lane markers and work with other systems that also use GPS data However, in prior art systems, the survey of the roadway is still needed and more importantly there are reliability issues due to signal blockage. Additionally, the application of DGPS using a low cost GPS receiver can result in position accuracy on the order of 1-5 meters. While such a level of accuracy is adequate for many applications, in lane-keeping approaches and other applications that require greater precision, systems that rely only on GPS or DGPS are not adequate to prevent imminent lane departure.
Accordingly, for the above reasons, the present invention is directed to a real-time, high-precision, DGPS-based, robust (due to the use of other navigation aids in addition to DGPS), automotive navigation system that can support a wide range of highway traffic applications. Specifically, the GPS based system is used to precisely monitor a vehicle""s location, in real time, relative to road lane boundaries. The present invention is directed to a GPS Roadside Integrated Precision Positioning System (GRIPPS).
A first embodiment of the present invention is directed to a real-time integrated navigation system for a vehicle. The system includes a GPS receiver, connected to a first antenna and receiving GPS data from satellites and outputting GPS position data, and a communications link, connected to a second antenna and to the GPS receiver, receiving range and carrier phase measurements from at least one base station. The system also includes navigation aids which provide relative position data of said vehicle, and a Kalman filter, connected to the output of the GPS receiver and the navigation aids, that integrates the GPS position data and the relative position data and outputs smoothed position data
In the system of the first embodiment the smoothed position data compensates for degradation, blockages or communication dropouts of the GPS data from the satellites. The navigation aids of the system can include at least one, and, preferably, at least two or more, of a distance measurement, e.g., odometer measurements or anti-lock braking system (ABS) wheel turns, heading measurements, and tilt measurements. Distance and heading measurements are preferred if only two navigation aids are used. More specifically, the navigation aids can include at least one, and, preferably, at least two or more, of anti-lock braking system wheel turns, electronic compass heading and pitch, and map vertical height that provides for the generation of a high rate, robust reference relative position. The real-time integrated navigation system for a vehicle provides smoothed position data that has a 2-cm position accuracy when GPS updates from good phase measurements are available.
In addition, the system of the first embodiment can include a lane departure module that receives the smoothed position data and utilizes stored map data to output a signal that is related to imminent lane departures of the vehicle. The system may have a spread spectrum radio modem as a part of its communications link and the second antenna can be a 900 MHz communications antenna to facilitate communications with the ground stations; other, better communications systems are commercially available.
A second embodiment of the present invention is directed to a method of providing real-time navigation data to a vehicle, having the steps of: receiving GPS data from satellites via a first antenna connected to a GPS receiver located on the vehicle and then receiving range and carrier phase measurements from at least one base station via a communications link connected to a second antenna and sending the range and carrier phase measurements to the GPS receiver. The method further includes the steps of outputting GPS position data from said GPS receiver to a Kalman filter and querying navigation aids to provide relative position data of said vehicle and providing the relative position data to said Kalman filter. GPS position data and the relative position data are integrated, using said Kalman filter, and the smoothed position data for the vehicle is output.
The method compensates for degradation, blockages or communication dropouts of the GPS data from the satellites. In addition, the queried navigation aids can include components providing at least one, and, preferably, at least two or more, of a distance measurement, e.g., odometer measurements or ABS wheel turns, heading measurements, and tilt measurements. Distance and heading measurements are preferred if only two navigation aids are used. More specifically, the components can provide at least one, and, preferably, at least two or more, of anti-lock braking system wheel turns, electronic compass heading and pitch, and map vertical height that provides for the generation of a high rate, robust reference relative position.
The method may also include providing the smoothed position data to a lane departure module and computing imminent lane departures of the vehicle based on stored map data and the smoothed position data. Preferably, the smoothed position data has a 2-cm position accuracy.
The method is also applicable where the communications link receives range corrections via a spread spectrum radio modem and the second antenna is a 900 MHz communications antenna.